Specification of Factors that Cause Seasonality of Birth in Schizophrenia: a Study for a Clue to the Preventive Measure Seasonality of births (winter increase and/or summer decrease) in schizophrenia has consistently been observed in a number of studies. Specification of the factors that cause the seasonality may provide a clue to elucidation of causal factors and development of preventive measures of the disease. We investigated several groups of schizophrenia patients born in different areas of Japan to obtain a clue to the specification. Also, a review of previous studies on the seasonality of births was conducted to look for promising candidates among the meteorological, infectious and other variables. The review of previous studies suggested that ambient temperature, duration of sunshine and infections such as polio, rather than influenza, might be good candidates of the factors (Tochigi, 2004). In the study of the Japanese patients, a significant decrease of summer birth compared
… More with the general population was observed, but the winter births were not increased in total patients, consistent with a previous Japanese investigation (Tatsumi, 2002). However, when the patients from the north area of the Honshu (or Tohoku District) were separately analyzed, an increase of the winter births, in addition to a decrease in the summer births, was. significant (Tochigi, submitted). When the Tohoku patients were compared with the patients from Nagasaki, a South-West area, the Tohoku patients showed augmented trends of increased winter and decreased summer births. These may suggest meteorological variables, rather than infections as a causing factor of the birth seasonality. Finally, schizophrenia patients from Hokkaido were studied, which generated controversial result. The seasonality was less apparent in the Hokkaido patients than the Tohoku, Nagasaki or other patients. The reason remains to be studied, but a lack of statistical power could be related. Additionally,. studies were conducted on effects of season on development of personality and future risk of crime offenses. As a result, winter births might lead to a decreased score of Agreeableness in healthy subjects (Tochigi, in press). Low agreeableness was observed in several mental illnesses in previous studies. Regarding crimes in youth, theft was associated with increased winter birth, while more violent crimes were related with decreased winter birth. Decreased winter birth was observed in substance abuse, which is closely related with violence. Less